1. Field of the Invention
The present invention relates generally to organic/polymer chemistry, and more particularly to novel luminescent compounds (polymers, oligomers, and monomers) which emit strong light when excited optically, electrically, and/or chemically; to processes for preparing said novel luminescent compounds; and to the use of said compounds in applications involving luminescence, e.g., as components of organic light emitting diodes (OLEDs), OLED displays, lights, as sensors, UV stabilizers, and the like.
2. Description of Related Art
Organic luminescence devices utilizing organic substances (either small organic molecules or polymers) have favorable prospects for the use in low-priced large-size full color displays, lasers, optoelectronic devices, photovoltaic devices, sensors, biotags, lights, and the like, and the demands therefor have been steadily growing. Such devices can emit light (e.g., organic light-emitting diodes, OLEDs, that make up displays) or respond to radiant energy (e.g., photodetectors). Compared with other tools for use in similar applications, organic luminescence devices offer many distinguishing advantages, such as their light weight, thinness, flexibility, wide range of colors, high contrast, fast response rate, low power consumption, high brightness, and no need for backlighting.
Organic luminescence devices may be classified depending on the molecular weight of their organic components and manufacturing processes: devices manufactured from low molecular weight compounds (small organic molecules) and devices manufactured using large molecular weight compounds (polymers). Low molecular weight compounds may be layered by vacuum deposition and may be easily purified to a high degree. In addition, color pixels may be easily obtained in a low molecular weight device. High molecular weight devices are more easily layered by casting, printing, dipping, spraying, lithography, and the like.
In organic luminescence devices, an organic active layer is generally sandwiched between two electrical contact layers (electrodes). At least one of the electrical contact layers is light-transmitting so that light can pass through it. The organic active layer may generate an electrical signal in response to light passing through the light-transmitting electrical contact layer, or it may emit light through the light-transmitting electrical contact layer upon application of electricity across the electrical contact layers.
Organic luminescence devices work through a double charge injection from two electrodes, i.e., holes are injected from the anode into the highest occupied molecular orbital (HOMO) of the emissive layer molecules (or first to the hole transport layer molecules if there is a hole transport layer, and then to the emissive layer molecules), and electrons from the cathode into the lowest unoccupied molecular orbital (LUMO) of the emissive layer molecules (or first to the electron transport layer molecules if there is an electron transport layer, and then to the emissive layer molecules), the hole and electron recombining in the emissive layer, thereby liberating energy as light.
Multiple layers between the two electrodes can make the light production more efficient (Tang et al. (1987) Applied Physics Letters 51: 913-915, and Burroughs et al. (1990) Nature 347: 539). The multiple layers may include one or more electron transport layers, and one or more hole transport layers. See Adachi et al. (1988) Japanese Journal of Applied Physics 27: L269-L271, and Mitschke and Bauerle (2000) J. Mater. Chem. 10: 1471-1507.
OLED displays may employ active matrix addressing or passive matrix addressing. In passive matrix displays there is an array of electrode lines for addressing individual pixels arranged in rows and columns; applying a voltage between a particular row and column energizes the pixel with that corresponding address. By analogy with active matrix liquid crystal displays, the polymer electronic device (display) can be addressed at individual pixels using, for example, a thin film transistor (TFT) device which switches that pixel on and off.
The use of organic electroluminescent materials as active materials in light emitting diodes is well known. Simple organic molecules such as anthracene, thiadiazole derivatives, and coumarin derivatives are known to show electroluminescence. Semiconductive conjugated polymers have also been used as electroluminescent materials, as has been disclosed in, for example, Friend et al, U.S. Pat. No. 5,247,190, and Heeger et al., U.S. Pat. No. 5,408,109. The organic materials can be tailored to provide emission at various wavelengths. Theoretically, it is possible to emit light of any color including red through blue by use of various organic compounds.
However, organic luminescence devices are frequently degraded by atmospheric gases, particularly oxygen and water vapor, and this instability can severely limit the working lifetime of the devices. In addition, when organic luminescence devices comprising conventional organic materials are continuously driven, the luminescence output reduces within a short time and the drive voltage has to be increased. Accordingly, there is an urgent need in the industry to improve the chemical stability/durability of layers in organic electronic devices that are sensitive to environmental elements. There is also a need to improve the durability as well as the life time of such devices. Additionally, it would also be beneficial to increase the initial luminous intensity/efficiency and color purity.
We have now discovered novel compounds, processes, and devices possessing high quantum yields which are easily prepared and modified generally by employing commercially available precursors, which help to address some of the above-mentioned deficiencies present in this area of technology.